This invention relates to a method for forming a reflector for an optical waveguide of the type mounted onto a generally planar substrate, which reflector redirects a light signal between a first path normal to the substrate and a second path parallel to the substrate. More particular, this invention relates to such method that includes sequentially irradiating a series of overlapping zones of the waveguide with intermittent laser beam flashes directed normal to the substrate that cooperate to form a smooth, angled surface for the reflector.
It has been proposed to produce an optoelectronic package that combines not only components connected by a metal circuit trace for processing electrical signals, but also optical components for processing light signals. The optical components may include devices for emitting light pulses, such as light emitting diodes, or for detecting light pulses, such as PIN detectors. The substrate carries a waveguide for laterally transmitting light signals to or from the component, similar to an electrical circuit trace for conducting electrical signals. The components are mounted onto the substrate overlying the waveguide and emit or receive the light signal along a path normal to the substrate, referred to herein as the normal path, which signals are then transmitted along a path through the waveguide that is parallel to the substrate, referred to herein as the waveguide path. Accordingly, a reflector is situated under the component and includes a mirrored surface at a preferred oblique angle of about 135 degrees relative to the waveguide path, for redirecting the light signal between the component and the waveguide, that is, between the normal path and the waveguide path.
A typical waveguide is formed of a narrow polymeric ridge applied to the substrate, which ridge may be either free standing or subsequently enclosed in a polymeric layer, provided that the adjacent polymer, like the air, has an index of refraction sufficiently distinct from the ridge to cause internal reflection to contain a light signal within the waveguide. Typical methods for forming the reflector generally comprise ablating an oblique surface in the waveguide ridge using a laser beam and thereafter depositing a reflective metallic film. One common method requires tilting the substrate relative to the laser beam. Since, in the production of optoelectronic devices, laser processing is employed to form several features in addition to the reflector surface, it is desired for convenience to ablate the reflector surface in conjunction with other laser forming operations. However, generally, the laser forming operations utilize a beam that is normal to the substrate. Thus, it is necessary to interrupt the laser operations to reorient the substrate in order to ablate the reflector surface. Furthermore, it is necessary to include corrective measures to compensate for the divergence of the beam to obtain an ablated surface at the desired angle. Another method utilizes a beam that is normal to the substrate and ablates the surface by progressively opening or closing a shutter interposed between the laser and the substrate. However, commonly available shutter mechanisms have not been entirely satisfactory to provide uniform, smooth movement needed to progessively ablate the oblique surface. Thus, there is a need for an improved method for forming a reflector surface in a waveguide using a laser directed normal to the substrate, and thus may be carried out in conjunction with other laser operations without reorientation of the substrate, while avoiding the difficulty of incorporating and smoothly operating a complex shutter mechanism within the laser device.